I have a project for a small computing room (not even big enough to be called small data center) where I will like to use the Mango ES solution, never used this product and I will like to start, can you give me a hand?

The room has two small ac units to control a rack temperature, the controlling logic is to be done with a controllers with I/Os (general functions like turning the ac on or off, rotating the equipment periodically, based on demand turn both ac units together, alarming)

I have identified the following equipment for this project

Mango ES

Controller with I/Os and sensors to act on the ac equipment, with Modbus RTU communication (can Mango ES be used to do this? or is this external controller necessary?)

3G router (the project requests the capability to send sms messages, can Mango do this without the 3G router?)

Is a Modbus RTU to IP gateway needed? or can the RS485 connection on the Mango ES be used to directly connect the RTU controller?

Controller with I/Os and sensors to act on the ac equipment, with Modbus RTU communication (can Mango ES be used to do this? or is this external controller necessary?)

While there has been a MangoES developed with analog inputs and digital outputs, it is no longer available on the https://buy.infiniteautomation.com website and there may not be more produced. So, a PLC with Modbus communication would be a better bet.

3G router (the project requests the capability to send sms messages, can Mango do this without the 3G router?)

You can use any 3G modem that works with arm32 Debian Linux, but the MangoES does not have any specific drivers installed for specific products by default. I believe people have contributed their solutions to this in various threads on the forum.

Is a Modbus RTU to IP gateway needed? or can the RS485 connection on the Mango ES be used to directly connect the RTU controller?

The MangoES's RS485 can be used for Modbus RTU.

Remote access to Mango through the internet and intranet is required

Mango provides cloud connect (though you would need a second Mango to be the VPN server), the MangoES has openvpn installed but no configured connections, and autossh (not installed) can be effective for persistent port forwarding through SSH tunnels. You have options!

For solving sms solutions I would personally use a service provider like www.smsapi.com which will send the sms messages for you instead of messing around with 3G modems and such because then you would have to consider that you will always have 3g connectivity and that drivers are also correctly working and such while using the provider you will only have to make sure that the controller is connected to the internet.

@phildunlap Is there another way of remotely accessing Mango? in the intranet I understand it can just be accessed through an IP address (am I right?), but from the internet? a public IP? (I need to keep this low cost).

You could expose its port to the internet for the easiest solution, or you could join a VPN as I suggested and perhaps have an Apache proxy taking care of SSL and routing whatever domain names you own. This help document could be of service there: https://help.infiniteautomation.com/proxy

If you were just to expose the port, you would either want to use a self-signed keystore or have a domain name so that you could use SSL, as described in this article: https://help.infiniteautomation.com/ssl

With regards to smsing and 3G routers, my recommendation is the Teltonika RUT955.
It is an amazing router with duel sim, internal GPS. It allows you to send sms's from the router via HTTP requests.
It is rugged and industrialised. cost is a little over $200.00